1. Field of the Invention
The present invention relates generally to an apparatus and method for assembling substrates. More specifically, the invention relates to an apparatus and method for assembling a flat panel display, such as a liquid crystal display.
2. Related Background Art
Liquid crystal displays have been widely used as displays for note-type and subnote-type personal computers since they are thin and light and have low electric power consumption. In recent years, with the improvement of performance of personal computers, it has been required to increase the display capacity and display area of the displays and to improve the picture quality thereof.
Liquid crystal displays are formed by filling a liquid crystal molecule into a space between two glass substrates, which are panel aligned with each other via spacers. A typical liquid crystal display is assembled by the following process.
First, a pair of glass substrates are vacuum held to a pair of upper and lower stages facing each other, respectively. In this case, on the surface of the glass substrate held on the lower stage, a plurality of electrodes are formed. In addition, a rectangular frame-shaped sealing material for defining a display region therein and spacers for holding a gap between the two glass substrates are arranged. On the glass substrate held on the upper stage, a counter electrode, a color filter and so forth are provided.
In this state, after the upper stage is moved downwards so that the two glass substrates face each other at a predetermined interval, the upper stage is moved in X and Y directions and rotated on Z axis to position the two glass substrates on the basis of positioning marks or the like.
Subsequently, the upper stage is moved downwards to a position at which the upper glass substrate contacts the sealing material and the spacers on the lower glass substrate. In this case, fine displacement between the glass substrates is caused by the contact resistance between the two glass substrates via the spacers and the sealing material, the rigidity and parallelism of the upper and lower stages in vertical movement, and the back crush of X, Y and .theta. drive mechanisms.
Therefore, the positioning between the two glass substrates is carried out by moving the upper stage in X, Y and .theta. directions again while the two glass substrates contact each other via the sealing material and the spacers. After this positioning, a pressure is applied so that the gap between the two glass substrates is a predetermined value, and a liquid crystal material is filled into a space between the glass substrates.
However, when the positioning between the two glass substrates is carried out by moving one of the two glass substrates while the two glass substrates contact each other via the spacers as described above, there is some possibility that the spacers strongly rub and scar the surface of an alignment layer and sink into the color filter layer or the like.
As described above, since it has been strongly desired to improve the picture quality of liquid crystal displays in recent years, fine scars caused during producing process are treated as bad picture quality to cause a decrease in production yield.